symbol.c: remove `Symbol#id2sym`.

In the ancient Ruby, symbols are represented by integers. In that era,
to get string representation from integers, we used `Integer#id2sym`
method. Later, `Symbol` was introduced, and `id2sym` was used for
compatibility. Today, no one uses `id2sym` any longer. It is described
in ISO 30170:2012 standard but I consider it as a mistake.

1 files changed, 0 insertions, 4 deletions

diff --git a/test/t/symbol.rb b/test/t/symbol.rb
index 5c674a9cb..4cb210757 100644
--- a/test/t/symbol.rb
+++ b/test/t/symbol.rb
@@ -17,10 +17,6 @@ assert('Symbol#===', '15.2.11.3.1') do
   assert_false :abc === :cba
 end
 
-assert('Symbol#id2name', '15.2.11.3.2') do
-  assert_equal 'abc', :abc.id2name
-end
-
 assert('Symbol#to_s', '15.2.11.3.3') do
   assert_equal  'abc', :abc.to_s
 end